Threaded Mode | Linear Mode

04-08-2008, 23:45

Dorn,

Original configuration on most (almost all vintage FC's) was four 6 volt batteries in series-parallel configuration. That's essentially two 12 voltbatteries each made up oftwo 6 volt batteries.Your configuration of three 12 volt batteries in parallel will certainly work but there are several considerations you should be aware of.First, when combining batteries whether in series or parallel, allof yourbatteries should bethe same voltage and amperage rating and age.

Second, batteries that are made for starting engines are generally rated in cold cranking ampsthe higher the cca'susually the more capacity of the battery to deliver a high current to start the engine. The batteries in older FC's are used for starting for sure, but,they are also used for supplying the 12 volt electrical power to thecoach for lighting etc. Batteries that are used for supplying electrical power for house use are generally rated in amp hours. A typical series pair of 6 volt batteriesmaking12 volts is rated at around 220 amp hours. Thereforethe original combination of four series/parallel wired 6 volt batteries provided 440 amp hours for house current. BTW there is a major difference in the construction of cranking batteries and batteries that provide lower current over long periods.

Since the 3208 engine is a relatively easy starter and therefore does notunder most conditions draw unusually high starting (cca) current for long periods, theseries parallel6 volt battery combination although not the greatest for starting is acceptable and works great forlighting and general coach power.

My recommendation to you is to change your battery set up to four 6 volt batteries in series parallel. If that doesn't set well with you, you should at the very least make sure that all of your 12 volt batteries are the same age and size. Most likely the smaller 12 volt battery is dragging down the performance of your newer larger 950 cca batteries.

As always you should ensure that all battery connections are clean and tight all the way to the starter and frame ground. Also ensure that the starter ground strap (cable from starter to the frame) is clean and tight. I found the ground strap on my coach originally ran over to the front compartment sheet metal and was not tight. I had intermittent starting problems so I changed tothe strap running to a clean frame connection and had no more problems.

Steve Anderson

79 FC 35

Poulsbo, Wa

In a message dated 4/9/2008 7:43:12 A.M. US Mountain Standard Time, dhetzel@... writes:

I'm having an odd issue with my 77FC35.

Alternator seems generally OK, 14-ish volts when engine running.

Shore power DC supply seems maybe a little less ok but does seem to run all the lights, etc.

Can freshly charge main batteries which are three 12v batteries, two 950 cranking amps, one smaller, all parallel.
(This doesn't look like the original config (was that four 6v series parallel?) but it's how the bird came to me)

On fresh charge to main batteries with external charger/booster the engine will start fine,
but after either driving around for a while or sitting for a while on shore power, the mains seem unable to
start the engine. I have put two brand new 950 cranking amp batteries in within the last week, so I'm
pretty sure it's not the batteries.

If I connect the charger to the batteries, it says within a minute that they are full, but the engine won't crank
unless I use the booster, then it cranks fine.

Any thoughts on what the issue might be and how to diagnose further?

Regards,

Dorn Hetzel
77FC35
Hogansville, GA

Planning your summer road trip? Check out AOL Travel Guides.